Contributing to the pollution has been a severe drought, which has lowered water levels, concentrating contaminants.
This year, a severe drought has lowered water levels in the reservoirs used to generate electricity, and mandatory rationing was imposed in June.
It destroyed at least half the crops on the Great Plains, lowered water levels in the Mississippi River so much that barges ran aground and created the conditions for a summer-long run of forest fires in the West.
It battered Mexico's Pacific-coast resort of Acapulco, and lowered water levels, enforcing draught restrictions on ships in the Panama canal.
But one official, Wang Jingquan of the Yangzi's Water Resources Committee, conceded that the dam had lowered water levels in two of the country's biggest freshwater lakes, making the impact worse.
But so far the three expeditions, backed by government support and international financing from the U.N.D.P., W.W.F. and other agencies, have lowered water levels in the lake by 3.63 meters, staving off what seemed like an imminent GLOF in 2010.
In the U.S., persistent drought on the Colorado Plateau has so significantly lowered water levels in the Colorado River and Lake Mead that Hoover Dam is fast approaching the day when it will no longer produce any power.
Four testing schemes for rising water level and three for lowering water level were done.
In comparison, maintaining a constant mining speed shortens the lifespan of bed separation, lowering water level and hydrostatic pressure, effectively mitigating hazards of bed-separation water burst.
A potential drop of soil pH from 5 to 2 may occur with serious consequences for paddy field and watercourses (huge acidity and dissolved metals at toxic levels) if pyrite is exposed to oxidation conditions (e.g. drainage system lowering water level below pyrite position).
